In many different food processing lines the use of an intermediate storage before a filling machine is employed. One example of such food processing line is UHT (Ultra High Temperature) processing of dairy products.
An aseptic tank is thus used for intermediate storage of UHT treated dairy products. Product flow and service media connections are placed in its valve and control module. An aseptic tank can be used in many ways in UHT lines, depending on plant design and the capacities of the various units in the process and packaging lines. Two examples are:
If one of the packaging machines unexpectedly stops, the aseptic tank takes care of the surplus product during the stoppage; or
simultaneous packaging of two products. The aseptic tank is first filled with one product, sufficient to last for a full shift of packaging. Then the UHT plant is switched over to another product, which is packed directly in the line of packaging machines.
One or more aseptic tanks included in the production line thus offer flexibility in production planning. Direct packaging from a UHT plant requires recirculation of a minimum extra volume of 300 litres per hour to maintain a constant pressure to the filling machines. Products that are sensitive to reprocessing cannot tolerate this and the required overcapacity must then be fed from an aseptic tank. One of the major advantages of an aseptic tank is that the product is only processed once, and in optimal conditions. This will always secure consistent, and best, product quality.
The optimum arrangement of UHT plants, aseptic tanks and aseptic packaging machines must thus be decided for each individual process.
One example of a contemporary aseptic intermediate storage tank is the Tetra® Alsafe® tank series.
Aseptic packaging has been defined as a procedure consisting of sterilisation of the packaging material or container, filling with a commercially sterile product in an aseptic environment, and producing containers that are tight enough to prevent recontamination, i.e. that are hermetically sealed.
For products with a long non-refrigerated shelf life, the package must also give almost complete protection against light and atmospheric oxygen. A milk carton for long-life milk must therefore be of high-quality carton board sandwiched between layers of polyethylene plastic. The term “aseptic” implies the absence or exclusion of any unwanted organisms from the product, package or other specific areas. “Hermetic” is a term used to indicate suitable mechanical properties to exclude the entry of bacteria into the package or, more strictly, to prevent the passage of micro-organisms and gas or vapour into or from the container.
It is as such of importance that the product is kept aseptic all the way to the filling machine.
Contemporary process lines employ a cluster of valves for regulating the flow from the intermediate storage and the filling machines to the filling pipes. Such end-valve clusters are generally recommended to be placed at least 7 m away from the filling machine and they are therefore sometimes placed by the intermediate storage tank to avoid any steam or fluids escaping the valves and contaminating the sterile filling area. The distance from the end-valve cluster to the actual filling line may thus be quite large. A nominal distance is 30 meters.
At the start of production, before the filling machine connected to the intermediate storage tank can start producing, it is necessary to purge the air from the storage tank to the filling machine, and therefore prime the line with product to the filling machine. When an intermediate storage tank is to be primed (i.e. to pour or admit product fluid into the tank to expel air and prepare for action) the filling line is primed all the way to the end-valve cluster or assembly. This is done after a tank has been cleaned, such as by Clean-In-Place (CIP) systems and Sterilised-In-Place, (SIP).
This results in that a large quantity of product, namely the quantity residing in the pipe leading from the end-valve cluster to the last filling machine—is filled unnecessarily. If it is not used later and goes to waste.
As cleaning is often made hundreds of times a year the loss is not negligible. For example, a nominal length of 30 meters from filling machine to end-valve cluster the piping holds approximately 55 litres of product. At a price of 1$ per litre of product and a cleaning of 250 times per year, a loss of $13,750 is caused every year by the cleaning alone.
One alternative solution of cleaning less would introduce a higher risk of a contaminated product and also a lower quality product as fouling of the piping would also affect for example the heat transfer coefficient which affects the hold time.
The alternative solution of recovering the product in the static leg after production and using the recovered product in future production also has a high risk of product contamination
The alternative solution of installing the end of line cluster close to the last filling machine has the risk of product contamination, and product, steam and CIP discharges interfering with the operation of the filling machine
Accordingly, an improved apparatus for intermediate storage would be advantageous for which such product waste is avoided.